Drugged driving: marijuana, prescriptions and DUI insurance

A conviction for driving under the influence of drugs generally lands on your record, and in your insurance file, the way an alcohol DUI does: as an impaired-driving conviction that can bring an SR-22 requirement, a steep surcharge and a hard look from underwriters. What differs is the road to the conviction. States define drug impairment in different ways, a prescription is not a safe harbor in most of them, and the science of testing for THC means that a driver can be charged without a number that proves impairment. We did not find an insurer or regulator that publishes a different rule for drug DUI than for alcohol DUI, so the safest working assumption is that the insurance consequences follow the conviction, not the substance.

Three ways states define drugged driving

Every state has a law against driving while impaired by a drug. Beyond that, the laws split. The Governors Highway Safety Association (GHSA) describes the law on its drug-impaired driving page, last updated October 2025 with state laws last reviewed by state highway safety offices in June 2025. It says drugged driving laws are "nuanced, difficult to enforce and prosecute and vary substantially by state," and groups them like this:

• An impairment standard. The state must show the driver was affected by a drug to a degree that made driving unsafe. Evidence is the driving, the officer's observations, field sobriety tests, a drug recognition evaluation and a chemical test. This is the baseline everywhere.
• Zero tolerance. It is illegal to drive with any measurable amount of a specified drug (or its metabolite) in the body, no impairment required. GHSA counts 16 states with zero tolerance laws for one or more drugs.
• Per se limits. It is illegal to drive with more than a set amount of a drug in the blood. GHSA counts 5 states with per se laws for one or more drugs.

For marijuana specifically, GHSA counts 18 states with zero tolerance or non-zero per se laws: 10 with zero tolerance for THC or a metabolite, 4 with zero tolerance for THC but no restriction on metabolites, 4 with specific per se limits for THC, and Colorado with a permissible inference law. A permissible inference lets a jury infer impairment from a specified THC level, which the driver can then try to rebut. The Insurance Institute for Highway Safety (IIHS), on a page it updated in August 2026, makes the same point: driving under the influence of marijuana is illegal in all 50 states, and where no limit exists, prosecutors rely on documented evidence of impairment and marijuana use.

A sample of how the GHSA table classifies marijuana impaired driving:

The table is a snapshot of one source at one time. Laws change each legislative session, and the same state can have a different rule for felonies than for misdemeanors, so confirm the current statute for the state where you drive. Colorado and Washington are among the states that legalized adult use early and wrote specific THC provisions; Arizona has a zero tolerance statute with a patient defense we discuss below.

How a prescription can lead to a DUI charge

Many people assume that a medicine taken as directed cannot support a DUI. The statutes in several states say otherwise. Washington's RCW 46.61.502 makes it an offense to drive while "under the influence of or affected by intoxicating liquor, cannabis, or any drug," and subsection (2) adds that the fact a person "is or has been entitled to use a drug under the laws of this state shall not constitute a defense." Note that alcohol, cannabis and other drugs sit in one section. The conviction is the same offense whichever substance was involved, which matters for how the record reads to an insurer.

Arizona's statute has the same idea. In Dobson v. McClennen, 238 Ariz. 389 (2015), which we read in the Caselaw Access Project archive, the Arizona Supreme Court described the state's DUI law as prohibiting driving "while under the influence of ... any drug ... if the person is impaired to the slightest degree," and noted that for that charge it "is not a defense ... that the person is or has been entitled to use drugs under the laws of this state." That description is from 2015, and Arizona has amended its marijuana laws since, so use it as an illustration of how such statutes are built.

What does the FDA say about which medicines are at issue? In a consumer update current as of March 2024, FDA lists these among the medicines that can impair driving: opioids, prescription anxiety medicines such as benzodiazepines, sleeping pills, muscle relaxants, some antidepressants, antiseizure and antipsychotic medicines, some cold and allergy medicines containing antihistamines, stimulants, and cannabis and cannabis-derived compounds including CBD. It advises taking a medicine for the first time when you will not need to drive and following the directions and warnings on the label.

The practical risks are:

• The first dose or a new dose. Many people do not know how a drug affects them until they take it.
• Combinations. Two medicines that are each safe alone can add up. Alcohol on top of a sedating medicine is a common one.
• Timing. Next-morning impairment after a sleep aid is a recognized problem.
• Over-the-counter products. An allergy tablet is a drug under these statutes.

None of this means taking medicine and driving is illegal. It means the legal test is impairment (or, in zero tolerance and per se states, presence), and the prescription label is not an answer to that test. A licensed attorney is the person to ask how your state treats a lawful prescription, since a defense available in one state may not exist in another.

The testing problem with THC

Alcohol is the benchmark for a reason: blood alcohol concentration tracks impairment well enough that a number can stand in for it. THC does not behave that way. IIHS summarizes research from Compton (2017): "THC levels in the body cannot reliably predict impairment," and low levels of THC "can be detected for several hours after peak impairment."

The National Highway Traffic Safety Administration reached a similar view in its 2017 report to Congress, Marijuana-Impaired Driving, which the federal transportation library's abstract summarizes as discussing the poor correlation of THC concentrations in the blood with impairment and the implication that setting per se levels is not meaningful.

The AAA Foundation for Traffic Safety put numbers on this in a 2016 study of drivers arrested for DUI, An Evaluation of Data from Drivers Arrested for Driving Under the Influence in Relation to Per se Limits for Cannabis. Among 4,799 subjects, the median blood THC concentration was 4.0 ng/mL, so half of those arrested on evidence of impaired driving were at or below that level, under the 5 ng/mL line that some states use. Considering all arrestees with evidence of cannabis use, only 30 percent would have been above a 5 ng/mL threshold. Within the group tested by drug recognition experts, the researchers found no correlation between blood THC and scores on individual impairment indicators, and concluded that a quantitative per se threshold for THC "cannot be scientifically supported."

Those findings point in two directions, and both matter to drivers.

• A low number is not a clean bill of health. A driver who is under a per se limit can still be charged under the impairment standard if the officer documents impairment.
• A high number does not prove impairment, but may be enough. In per se states, exceeding the limit can itself be the offense. Washington's statute sets 5.00 ng or higher within two hours after driving, allows blood drawn later to be used as evidence of the level within two hours, and gives drivers an affirmative defense if they consumed cannabis after driving and before the test.

The timing detail has a consequence for a driver stopped after a crash. A blood draw may happen hours later, when active THC has changed. That cuts both ways, and the legal fight is usually about what the number means. It is a topic for a lawyer, not an insurer.

Medical cannabis patients

Legal medical use does not by itself protect a driver. GHSA's table lists several states where medical marijuana is legal and driving with THC or its metabolite is still a zero tolerance offense, including Pennsylvania and Utah. Others have written patient protections into their laws, and the details differ.

Arizona shows how a patient defense can be built. In Dobson, two medical marijuana cardholders were convicted under the statute that prohibits driving with any amount of a listed drug or its metabolite in the body. The Arizona Supreme Court held that the state's medical marijuana act "does not immunize a medical marijuana cardholder from prosecution" under that provision but "instead affords an affirmative defense if the cardholder shows that the marijuana or its metabolite was in a concentration insufficient to cause impairment." The same opinion confirmed that the act does not allow driving while under the influence of marijuana. So a patient can be charged, and the card matters to the defense without ending the case. The burden of showing the defense sits with the driver.

For insurance, this means a patient who is charged but convicted of the less serious offense may face a different record entry than one convicted of an impairment-based offense. Which conviction code ends up on the motor vehicle report is what the insurer reads.

What insurers do after a drug-related conviction

Insurers rate the conviction they see on the driving record, not the courtroom story. A DUI is a major violation in nearly every rating plan, and an impairment conviction typically triggers the steepest surcharge tier or a decline. North Carolina's published rating plan, for instance, assigns its highest point tier, 12 points and a 340 percent increase, to driving while impaired, according to the state insurance department. That page does not distinguish the substance, and we did not find evidence that insurers price drug and alcohol convictions differently, though we could not review every company's underwriting rules.

Three consequences are standard once a DUI conviction is on the record.

1. An SR-22 or similar proof. States that require proof of financial responsibility after an impaired-driving conviction typically want your insurer to file a certificate. Washington's licensing department says the requirement generally runs three years from the date you are eligible to reinstate your license, and it accepts an SR-22 from an approved insurer, a certificate of deposit of at least $60,000 or a liability bond of at least $60,000. Other states differ in form and length. Our guide to SR-22 insurance explained covers the filing.
2. A move to nonstandard coverage. Many standard insurers decline or non-renew after a DUI, which leads drivers to nonstandard auto insurance companies. See Nonrenewal after a ticket or DUI: your rights and next steps for your rights.
3. Added license conditions. Some states require an ignition interlock device for certain offenders. A DUI timeline: from arrest to getting insured again walks through the sequence.

The effect can last years, since the conviction stays in the look-back windows insurers use. How long varies by company and state. Our guide to Car insurance after a DUI covers pricing and options, and high-risk car insurance: options when insurers say no explains the market when standard insurers say no.

An arrest is not a conviction. Insurers generally act on convictions, and what happens to the charge (dismissal, reduction, a plea to a lesser offense) decides what the record shows. That reduction can be worth real money on insurance, but it is a legal strategy with its own risks, and a licensed attorney is the person to discuss it with.

Coverage questions after a crash

If a drug-impaired driver causes a crash, three separate insurance questions arise.

• Do the injured people get paid? Liability coverage exists to pay people the insured harms, and standard personal auto policies do not generally list impairment as an exclusion to liability coverage. Read your own policy's exclusions, because wording differs and a few circumstances (intentional acts, certain business uses) are excluded. Our article does car insurance pay when the at-fault driver was drunk? goes through the principles, which apply equally to drug impairment.
• Does the impaired driver's own damage get paid? Collision coverage responds to the policy's terms. Impairment may support other consequences, such as a claim investigation, a rate increase at renewal or a nonrenewal, even where the claim itself is paid.
• Can the driver be sued for more than the policy limit? Yes. Impaired driving can raise a claim for punitive damages in some states, and punitive damages are not insurable in some states. See punitive damages in car crashes: drunk driving and insurance for how that works.

Tell your insurer about a crash promptly regardless of impairment. Delay is its own problem, and an insurer cannot defend a claim it does not know about.

A hypothetical: the same blood result in two states

Say two drivers each take a prescribed medication as directed, are stopped after a minor crash and give blood that shows the drug. The drivers are hypothetical, and the example is a simplification of two statutes.

In a state like Washington, where the statute says entitlement to use a drug is no defense to a charge of driving under the influence of or affected by a drug, the prescription does not end the case, and the question is whether the driver was affected. In a zero tolerance state with a defense for use as prescribed, the question can turn on whether the driver took the drug as a licensed practitioner prescribed it, as Arizona's statute provided when Dobson was decided. The same blood test, the same label, two different legal questions.

For insurance, both drivers face the same problem if convicted: an impaired-driving conviction on the record. If the first driver is acquitted and the second pleads to a lesser offense, their records differ. The details of those outcomes are decisions for a lawyer, but the effect on premium is large enough that it should be part of the conversation.

Questions to ask after a charge

1. What exact offense name and statute number will appear on my driving record if I am convicted, and does the record say "drug" or only "impaired driving"?
2. How long will the conviction stay in my state's look-back window for insurance, and when does the SR-22 requirement (if any) begin and end?
3. Does my current insurer non-renew for this conviction, and what is its notice period?
4. If I am a medical cannabis patient, does my state offer any affirmative defense, and what must I prove?
5. If a lesser offense is offered, how does an insurer rate it compared with a DUI?

Common questions

Is a drug DUI treated differently from an alcohol DUI by insurers?

We found no published insurer or regulator rule that distinguishes them. Insurers rate the conviction on your motor vehicle report, and in states like Washington drugs and alcohol sit in the same statutory offense. Underwriting rules differ by company, so ask yours how it classifies the specific conviction on your record.

Can I be charged if my THC level is below the state limit?

Yes, in a state with an impairment standard. A per se limit is one way to prove the offense, not the only way. If an officer documents impairment, the driver can be charged regardless of the number, and the AAA Foundation's data show why the number is an imperfect guide.

Does a prescription protect me?

Not on its own in many states. Washington's statute says entitlement to use a drug is no defense to an impairment charge. Some states have a defense for use as prescribed in certain zero tolerance charges, as Arizona did under Dobson. Ask a licensed attorney how your state handles it.

Will my insurer find out about an arrest?

Insurers generally learn of convictions through the driving record. An arrest without a conviction may not appear. A license suspension that follows an arrest can, though, so check what your state's record shows.

How long does a drug DUI affect my rates?

It varies by insurer and state. SR-22 requirements often last about three years, as in Washington's general rule, and insurers' look-back periods for DUI can be longer. Our guide to Car insurance after a DUI covers typical timelines.

Key takeaways

• States define drugged driving three ways, by impairment, zero tolerance or a numeric per se limit, and GHSA's table shows the mix changing from state to state.
• A valid prescription is not a defense to an impairment charge in states like Washington, and the FDA lists many common medicines that can impair driving.
• THC is hard to test: the AAA Foundation found no scientifically supportable per se threshold, so charges often rest on observed impairment.
• Insurers rate the conviction on the record, so expect SR-22, a major surcharge or a move to nonstandard coverage, just as with alcohol.
• Details of a charge, a defense or a plea belong with a licensed attorney, and your state insurance department can explain how your insurers must treat the result.